250 
The composition of the rock is then as follows: 
50°83 Albite. 
38°54 Quartz. 
0:42 Silica soluble. 
1:23 Water. 
9°17 Bases dissolved (8°96 plus 0°21.) 
100-19 
4, This specimen consisted of white and very light brown grains 
agglutinated apparently by a light green, and in some places black, 
compound of copper. The grains of feldspar seemed to have been 
decomposed and replaced by chrysocolla. It contained no carbonic 
acid. 
88°69 Insoluble in acid. 
75°52 $10;(75:95—0°43) 
13°17 Bases combined with silica. 
Bases undissolved and combined with silica. 
Al,O;=9°52 
NaO =3:58 
13°10 
The difficulty of calculating the constitution of this rock is 
much greater than in the preceding samples, as we find more 
than two minerals. The soda in forming feldspar would 
require, 
Al.O; = 5°95 
NaO = 38°58 
SiO; = 20°80 
30°33 Albite. 
The rest of the alumina, as a remnant of decomposed feld- 
spar, requires all its silica. 
Al,O; = 8°57 
SiOs s— + 251 
16°08 Clay. 
The copper, which is not in the form of carbonate, calculated 
